Historically, automotive vehicles have been provided with mechanical speedometers in which the rotation of a wheel of the vehicle or of a drive component of the transmission is transmitted as a torsional impulse on a cable. The torsional force applied to the cable is typically transmitted to a needle in the instrument panel which is deflected across a scale to indicate the speed at which the vehicle is traveling.
Various attempts have been made to provide digital speedometers to replace the conventional mechanical analog variety of speedometers. All previous attempts to provide such digital speedometers have involved certain disadvantages that have prevented their commercial acceptance. One principal disadvantage with such systems has been the requirement for a signal generating system independent of the conventional mechanical speedometer system with which automotive vehicles are supplied as matter of course. The requirement for a separate signal generator adds considerably to the expense of a digital speedometer and necessitates the inconvenience and disadvantage of adding a data gathering system to the vehicle which the vehicle is not designed to accomodate.
Another distinct disadvantage of digital speedometers currently available is the inflexibility of their design for adaptation to vehicles of different design. The wheel size, transmission ratio, and voltage and current characteristics in the electrical systems of different styles of automotive vehicles has heretofor required a different calibration of a digital speedometer for the particular vehicle with which it is to be used. Such calibration in the past has been provided by using programmable storage devices, thumbwheel switches, and other cumbersome, expensive and inconvenient means for adapting a particular digital speedometer for use with a particular vehicle.